Chazal say that "everything is in the hands of heaven besides for the fear of Heaven". How does this fit in with the idea that we should just give over the fight to Hashem? Doesn't "free-choice" mean that Hashem gives the fight over to us?
Hi Snibril! You asked a question that really requires a whole discussion, but for now let me try to answer in short.
1) Our free choice is only in our "ratzon - desire". We have free-will to get pulled after the desires of our body and make that our ratzon; or we can get pulled after our soul and our wisdom and make that our ratzon. "Hishtadlus" (practical efforts) are part of this - because if we truly want something we will act towards it. We need to put our ratzon into action to make it real. But whether we succeed or not is only in the Hands of Hashem.
2) We often have free-choice to stay out of a situation, but once we get ourselves into the situation already, we may not have free-choice any more.
3) It goes without saying that every person's free-choice is only within certain limits, depending on his level. For example, if someone never learned a word of Torah in his life and has always been wasting his time on nothingness, he obviously doesn't have free-choice to not be mevatel Torah at all. Of course, with time he can get there, but right now there's nothing to talk about. The same applies to a lust addict. In fact, the Ohr Hachaim Hakodosh says explicitly that once someone got used to sinning in this area, he can't stop al pi derech hateva (i.e. by using natural means), rather only by using the power of Hashem (see this amazing peice from the Ohr Hachayim over here). When we have the wisdom to realize that the lust is killing us and we run to Hashem to save us, then He makes a miracle for us and saves us from the addiction.